The present invention relates to a butterfly valve apparatus which comprises a valve housing and a valve plate positioned within the housing and which is adapted to be mounted on pipes or the like for conveying fluids, the valve plate being fixed to a valve stem rotatable by rotating means to open or close the fluid passage in the pipe and to thereby permit or stop the flow of fluid.
Various butterfly valve apparatuses of the type described above have heretofore been provided in which the valve plate is fixed to the valve stem the conventional construction being such that the valve stem is rigidly connected to rotating means by a coupling member. The valve stem is supported by bearing members on the valve housing, with a minute clearance formed between the valve stem and the bearing members as required for lubrication. Accordingly, with opening or closing of the valve plate and in response to a change in the direction of flow of the fluid within the valve, the valve stem is movable by a small amount corresponding to the clearance, with the result that the fluid pressure on the valve plate acts not only on the bearing members for the valve stem but also on the coupling member or on the rotating means which is rigidly connected to the valve stem, thereby subjecting the coupling member or the gear surfaces and shaft of rotating means to an objectionable high pressure, which accelerates the abrasion of gears and bearings and increases the load. Consequently, smooth rotation is impaired or, conversely, the gears can not mesh with each other to a full extent, failing to effect the desired transmission of torque.